avoid reentrant lock acquire when ThreadIds run out
avoid reentrant lock acquire when ThreadIds run out

aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust